constant vs periodical

constant

adj
  • Consistently recurring over time; persistent. 

  • Firm; solid; not fluid. 

  • Unchanged through time or space; permanent. 

  • Steady in purpose, action, feeling, etc. 

  • Bounded above by a constant. 

noun
  • A quantity that remains at a fixed value throughout a given discussion. 

  • Any property of an experiment, determined numerically, that does not change under given circumstances. 

  • That which is permanent or invariable. 

  • An identifier that is bound to an invariant value; a fixed value given a name to aid in readability of source code. 

periodical

adj
  • Periodic. 

  • Published at regular intervals of more than one day, especially weekly, monthly, or quarterly. 

  • Of, or relating to such a publication. 

noun
  • A regularly issued thematic publication that contains the most current information in its field, often the primary means for communication of original scholarship or creative work at the cutting edge of research in its field. 

  • A publication issued regularly, but less frequently than daily. 

How often have the words constant and periodical occurred in a corpus of books? (source: Google Ngram Viewer )